Syringes containing a frozen fluid, such as premixed curable liquids, epoxies, pastes, thixotropic liquids, and adhesives, are used in applications including, but not limited to, semiconductor and optoelectronic packaging. The syringe, also referred to by conventional terms such as cartridge, barrel, tube, or reservoir, dispenses the frozen fluid after it is thawed. Premixing adhesives and pastes eliminates handling and weighing individual components, the mess associated with mixing these components, testing before and after mixing for quality assurance, training employees to handle hazardous raw materials, and the need to dispose of hazardous wastes. The syringe is filled with fluid at room temperature, frozen at temperature below the fluid's freezing point, and shipped in a thermally insulated container from the manufacturer at a temperature of about −40° C. to about −80° C. (i.e., on dry ice). The end user stores the frozen syringe and fluid in a low-temperature freezer at a temperature less than the fluid's freezing point. Low temperature storage extends the working life, delays aging and prevents curing, which thereby extends or prolongs the shelf life of the fluid. The end user warms the syringe and fluid to ambient temperature shortly before dispensing the fluid from the syringe. After the fluid is dispensed, the syringe is discarded.
Syringes containing such frozen fluids are susceptible to a phenomenon known as freeze-thaw voiding when thawed from the frozen state. Specifically, the frozen fluid and the syringe each shrink in dimensions or contract when frozen. Differential shrinkage arises from the different coefficients of thermal expansion of the material forming the syringe and the fluid. During thawing, the sidewall of the syringe warms faster than the frozen mass of fluid held inside the syringe. Because the syringe sidewall and the frozen mass of fluid do not thaw simultaneously, the sidewall expands first and pulls away from the frozen fluid. This separation creates an air-filled space between the frozen mass of fluid and the sidewall. As the fluid thaws and re-wets arbitrary regions of the syringe sidewall, air bubbles or pockets are surrounded by the regions of fluid and subsequently trapped between the fluid and sidewall. The trapped air pockets, termed by some as freeze-thaw voids, have an adverse impact on the dispensability of the fluid. Dispensing fluid laced with air-filled voids causes dispensing inconsistencies, such as tailing, dripping, dispense voids, and weight variations.
For some fluids, freeze-thaw voids are observed to form in the vast majority of fluid-filled syringes. Depending upon the type of fluid, the voids may self-alleviate by migrating to the vicinity of the syringe plunger and may be passed rearwardly past the periphery of the plunger. For other fluids, the voids have fixed locations and are not self-alleviating. Then, either the entire syringe is discarded without use to avoid the potential for dispensing the voids or the fluid is carefully dispensed from the syringe without dispensing the voids. In this latter circumstance, only a portion of the fluid is dispensed and the syringe is ultimately discarded with unused fluid remaining inside the syringe.
It would therefore be desirable to provide a syringe for fluids that reduces or minimizes the incidence of freeze-thaw voiding.